The capture and storage (CSS) of waste materials continues to be a problem is many industries. In the nuclear industry, the capture and storage of fission gases is important in both the disposal of large quantities of high level radioactive wastes generated in the reprocessing of spent power reactor fuel and from nuclear reactor accidents. It is generally accepted that the most promising approach is to convert these radioactive wastes to a dry solid form which would render such wastes chemically, thermally and radioactively stable. This problem of dry solid stability is closely related to the safety of human life on earth for a period of over 20,000 years. For example, radioactive wastes contain isotopes including 129I, 90Sr, 240Pu, and 137Cs, whose half-lives are >15 million years, 29 years, 66,000 years, and 30 years respectively. These isotopes alone pose a significant threat to life and must be put into dry, solid forms that are stable for thousands of years. The solid radioactive waste form must be able to keep the radioactive isotopes immobilized for this length of time, preferably even in the presence of a water environment.
For radioactive gases, one present immobilization route is the so-called dry solids approach which involves the method of fixation of waste materials in glasses via melting glass procedures. This approach offers some improvement regarding isolation and decrease in the rate of release of radioactive elements when the outer envelopes or containers are destroyed. However, standard nuclear waste glasses (such as borosilicate glass) glasses with high chemical durability and low alkali ion conductivities are melted at very high temperatures, e.g., 1800° C. and higher. Such high melting processes are economically unsound and moreover, cause a dangerous problem due to the volatilization of pernicious radioactive materials. Additionally, none or very small amounts of gaseous radioactive materials are further trapped in case of volatilization during glass formation.
In nuclear power accident clean-up, the removal of radioactive Cs and/or Sr from seawater or containment fluids is a critical issue. Other scenarios include the removal of uranium (U) based compounds and ions from water systems in case of accidents of for reuse, and/or in the act of resource extraction (in a sense ocean water “mining”).
In the power generation industry, and in particular coal fired power generation, the generation and release into the atmosphere of large quantities of CO2 remains an area of concern. A number of CO2 CCS technologies have been developed. One method for CCS uses metal oxide solutions, such as potassium or magnesium oxide, to remove CO2 from flue gas or other CO2 containing vent gases. The general capture mechanism involves reaction of the metal oxides with CO2 to form metal carbonates. These carbonate salts can either be land-filled, or be regenerated via oxidation to form a concentrated CO2 stream that can be compressed and injected into geological formations for storage.
Present methods of gas capture, and in particular, waste gas capture, lack the ability to store the captured gas in a stable form for a lengthy period of time. In particular, present day storage does not provide sufficient isolation and immobilization of such waste material, sufficient long-term resistance to chemical attack by the surroundings, and sufficient stability at high temperature.
In addition, a process for fixating radioactive materials inside a dry solid form having high resistance to leaching and other forms of chemical attack would not only be suitable for the containment, interim storage and possible eventual disposal of radioactive nuclear wastes.
The need remains, therefore, for a method and system for the capture and storage of gases that provides a high degree of stable containment. The need also remains for a method of forming waste forms below the volatilization temperature of the captured waste.